Battery operated devices, such as cellular phones, radios, MP3 players, personal data appliances, pagers and small sized computers, may suffer from short power failures. The short power failures can occur for various reasons, including but not limited to a relative movement between the battery and its connectors.
Short power failures can cause a device to enter a unknown state, to lose previously stored information, to lose synchronization with other devices, and the like.
In order to reduce, minimize or even to eliminate the negative effects of short power failures prior art device monitored the level of the supply voltage. Once the supply voltage was below a certain threshold a failure recovery sequence was applied.
Typically a power source such as a battery is connected to a power reservoir. A typical power reservoir includes a capacitor.
The power reservoir is charged by the battery and provides supply voltage to various components of the device during short power failures. Typically, due to size and cost limitations, the power reservoir can supply power for a relatively short period.
The following patents, which are incorporated herein by reference, describe failure recovery devices and methods that detect a power failure by comparing the level of the supply voltage to a fixed low voltage threshold: U.S. Pat. No. 6,226,556 of Itkin et al., U.S. Pat. No. 5,739,596 of Yasutoshi et al., and GB patent 2335569A1 of Rushinek et al.
The low voltage threshold is set above a power failure level. Once the supply voltage reaches the power failure level the device ceases to operate and is actually shut down.
The low voltage threshold has to be set at a certain distance above the power failure level such as to facilitate a completion of a power failure detection and recovery measure sequence such as storing critical information in an SDRAM or shutting down non-vital components.
On the other hand, in order to allow prolonged operation of the device the low voltage threshold power has to be relatively low.
There is a need to provide efficient methods and devices for failure recovery.